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Filesystem Hierarchy Standard (FHS)

I wanted to begin with the Filesystem Hierarchy Standard (FHS) which is currently at version 3.0. The standard can be referenced below as well as at http://refspecs.linuxfoundation.org/fhs.shtml.

Filesystem Hierarchy Standard 3.0

When I first began using Linux, I realized that all the files and directories were arranged in a particular way. I wondered why Linux always seemed to have this organization and what each directory was for. After many years of just “going with it” I finally came across this resource. It was originally written in 2004 but version 3.0 was released in 2015. Its goal is, “to support interoperability of applications, system administration tools, development tools, and scripts as well as greater uniformity of documentation for these systems.”

The hierarchy is as follows:

Directory Description
bin Essential command binaries
boot Static files of the boot loader
dev Device files
etc Host-specific system configuration
lib Essential shared libraries and kernel modules
media Mount point for removable media
mnt Mount point for mounting a filesystem temporarily
opt Add-on application software packages
run Data relevant to running processes
sbin Essential system binaries
srv Data for services provided by this system
tmp Temporary files
usr Secondary hierarchy
var Variable data
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CompTIA Linux+

I am starting my journey to become CompTIA Linux+ certified! Technically, I started on February 1, but am just now writing this. I have always been curious about Linux and dabbled here and there; I just have never dived in deep enough to be proficient. I want to change that. As an end user, I can get by in a Linux GUI and somewhat on the command line. I want to have greater knowledge than that. I want to be able to administer Linux systems on a professional level with confidence and without having to have Google opened up all the time. I would like to be able to add ‘Linux Administrator’ to my résumé under skills someday.

For this test, I am again going to use ITPro.tv (https://itpro.tv/) combined with Safari Books Online (https://www.safaribooksonline.com/) and Quizlet (https://quizlet.com/). Between the videos, books, practice tests, practice labs, and online flashcards, I have a ton of resources to take the deep dive and stay constantly engaged. I feel the fastest and most successful method of learning is to have multiple inputs. This has proven very successful for me. I also compare and contrast real-world experiences to something I am learning and that helps reinforce the material for me.

I am excited for this opportunity and look forward to getting this accomplished!

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Benefits of Switch Stacking and Chassis Aggregation

Switch stacking, known as Cisco StackWise on Cisco products, is a technology that connects multiple switches into one logical switch. By using stacking technology you get a decrease in administrative overhead and less blocked ports from Spanning-tree Protocol (STP).

You can add switches to gain port density and you can add them over time. This provides room to grow and decreases up front costs. Since the switch now appears as one logical switch, you only need to assign one management IP to it rather than individual IPs to each access switch. The administrative burden is lessened as well as you can go into one interface rather than into individual management consoles.

There is a master switch, called the stack master (which is elected), that manages the stack. The remainder of switches communicate via special interconnect cables. EtherChannel can still be used and will eliminate STP. StackWise technology can support up to nine switches.

Verify

To find how the stack ports are connected.

Switch#show switch stack-ports

To see the switch neighbors.

Switch#show switch neighbors

 

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Using Local SPAN to Troubleshoot and Resolve Problems

A Switched Port Analyzer, or SPAN, is a way that you can monitor traffic. Back when networks used hubs, all traffic was visible because a hub just repeated the traffic out every port except the one it came in on. When switches were introduced, SPAN functionality was introduced to accommodate.

It is common to set a SPAN port up to a device with Wireshark to analyze network traffic. If you are going to monitor the traffic from a single management workstation, you will need two network interfaces cards (NIC) since SPAN traffic is not able traverse the same line as data. If you are only using the management station to monitor the traffic, you can use the single NIC. SPAN actually copies the data from one port to another that you specify. You can monitor egress traffic, ingress traffic, or a combination of the two.

Configure

When you configure a SPAN session, your source and destination ports cannot be the same. You will configure the source, what you want to monitor, to a destination interface, where you will monitor. The following is an example of the syntax you would use to configure a SPAN session.

Switch#configure terminal
Switch(config)#monitor session session-id source interface-id
Switch(config)#monitor session session-id destination interface-id

Verify

Switch#show monitor
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ICMP Echo-Based IP SLA

Internet Control Message Protocol (ICMP) is a commonly used utility to test Layer 3 connectivity between devices. A Service Level Agreement (SLA) is a target that must be met; there is no set criteria for an SLA. ICMP echo-based IP SLA is a way to monitor end-to-end response time between Cisco devices using IPv4 or IPv6. According to Cisco, “Response time is computed by measuring the time taken between sending an ICMP Echo request message to the destination and receiving an ICMP Echo reply.” Using IP SLA ICMP echo to test far-end devices is much more practical than pinging manually.

Configure

Router#configure terminal
Router(config)#ip sla operation-number
Router(config-ip-sla)#icmp-echo {destination-ip-address | destination-hostname} [source-ip {ip-address | hostname} | source-interface interface-name
Router(config-ip-sla-echo)#frequency 300
Router(config-ip-sla-echo)#end

The ‘ip sla operation-number’ begins configuration for an IP SLA operation and enters IP SLA configuration mode. Icmp-echo defines an ICMP Echo operation and enters IP SLA ICMP Echo configuration mode.  The frequesncy sets the rate at which a specified IP SLAs operation repeats.

Verify

You can verify the IP SLA configuration with the following show commands.

show ip sla configuration
show ip sla statistics

Reference

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipsla/configuration/15-mt/sla-15-mt-book/sla_icmp_echo.html

CCNA ICND2 Study Guide, 3rd Edition by Todd Lammle

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Connecting to IPv6 Websites by IP

Internet Protocol version 6 (IPv6) request for comments (RFC) 1883 (https://tools.ietf.org/html/rfc1883) came out in December 1995. That’s 22 years ago! So how do you connect to an IPv6 address without using a Domain Name Server (DNS)? It’s only slightly different than Internet Protocol version 4 (IPv4). You do need to make sure you have an IPv6 address before starting. If you are unsure that you have one, you can do an ipconfig (on Windows), ifconfig (on *nix), or download an app for you mobile device.

In IPv4, you can just type in the dotted decimal address into the Uniform Resource Locator (URL) address bar.

https://67.247.154.182

IPv6 does not use dotted decimal addresses though, it uses colon separated addresses that look like this: 2604:6000:1009:c2a2:6a05:caff:fe46:e2b5. The colon in the URL address bar actually serves a purpose. The left of the colon identifies the protocol to use. Common protocols used in the browser are http, https, and ftp. In order to use an IPv6 address without confusing the browser, you need to wrap the IPv6 address in square brackets.

https://[2604:6000:1009:c2a2:6a05:caff:fe46:e2b5]

This is also specified in RFC 2732 if you want to learn more. (http://www.ietf.org/rfc/rfc2732.txt)

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Point-to-Point Link

Configure

To configure a Point-to-Point link, you will configure the serial interface just like you would an Ethernet interface. In addition, you need to use the no shutdown command because interfaces are down by default on a router. The other difference is that you need to have a clocking mechanism in place. Clocking takes place on the Data Communications Equipment (DCE).

Router#configure terminal
Router(config)#interface serial 0/0/0
Router(config-if)#ip address ip-address subnet-mask
Router(config-if)#no shutdown
Router(config-if)#end

The default encapsulation type is High-Level Data Link (HDLC) protocol. To change it, you specify while in the interface configuration mode.

Router#configure terminal
Router(config)#interface serial 0/0/0
Router(config-if)#encapsulation ppp
Router(config-if)#end

Verify

The following verification command identifies the Data Terminal Equipment (DTE).

Router#show controllers serial 0/0/0 | include V.35
DTE V.35

The following verification command identifies the Data Communications Equipment (DCE).

Router#show controllers serial 0/0/0 | include V.35
DCE V.35, clock rate 2000000

This next command will display the properties for the serial interface. From it, we can see the encapsulation protocol is set to High-Level Data Link (HDLC) protocol.

Router#show interfaces serial 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is WIC MBRD Serial
Internet address is 192.168.255.2/30
MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set

This next command is to verify that the Point-to-Point protocol encapsulation is set on the serial interface. LCP in the output is for Link-Control Protocol.

Router#show interfaces serial 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is WIC MBRD Serial
Internet address is 192.168.255.2/30
MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, LCP Open
Open: IPCP, CDPCP, loopback not set